1. Field of the Invention
This invention relates to a ceramic honeycomb structural body used as a catalyst carrier for purification of an exhaust gas from an internal combustion engine for automobiles, a filter for purification of fine particles, or a catalyst carrier for purification and/or deodorization of an exhaust gas using various gases or petroleum as a fuel.
2. Related Art Statement
Heretofore, the ceramic honeycomb structural body used as a catalyst carrier is required to mainly satisfy the following two conditions:
(1) the geometric surface area per volume (simply referred to as a surface area hereinafter) of the ceramic honeycomb structural body is increased to improve the purification performance;,and PA1 (2) the pressure loss of combustion gas is decreased to reduce energy required for permeation.
As a method for simultaneously satisfying these two requirements, if it is generally intended to make the cell density of the ceramic honeycomb structural body constant. A method has been proposed wherein the thickness of the partition wall inclusive of its crossing portion is made uniformly thin over the whole of the structural body. Another method has been proposed wherein the thickness of the partition wall is regularly thinned toward a passing center of an exhaust gas as disclosed in Japanese Patent laid open No. 54-110,189.
Furthermore, U.S. Pat. No. 4,404,007 proposes a method wherein a plurality of projections are irregularly arranged on the inner wall face of the cell to disturb the flow of the exhaust gas passing through the through-hole, thereby improving the purification performance of the exhaust gas, for example, the collection ratio of fine particles.
Moreover, European Patent Application laid open No. 191982A proposes a method wherein a fin is integrally united to the inner wall face of the partition to increase the surface area of the cell for improving the purification performance.
When the thickness of the partition wall is made thin over the whole thereof, however, there is a problem that as the thickness of the partition wall decreases, the partition wall is apt to be deformed during the shaping and the mechanical strength thereof lower.
In the method disclosed in U.S. Pat. No. 4,404,007, the surface area of the ceramic honeycomb structural body increases owing to the presence of the projections on the inner wall face of cell, but the disturbance of the passing gas undesirably occurs, thus considerably increasing the pressure loss.
In the method disclosed in European Patent Application laid open No. 191982A, the arrangement of the fin on the partition wall increases the surface area but brings about the increase of pressure loss as in the case of U.S. Pat. No. 4,404,007.